Temperature on the Rate of Growth in Pisum sativum. 31 
To illustrate the absence of any ‘ stimulatory ’ effect, Experiment 2 may 
be cited in full. 
Time. 
Growth. 
'J' ^ 
2-49, 3-19, 3-25, 3*31, 3-37, 3*43* 3‘49> 4* I 9> 4*49- 
i*6 0-3 0*3 o*3 0*3 0-4 i-6 i-8 
The fifth reading in light is due to the inaccuracy in reading, readings 
being ‘ up to 5 one micrometer division (0-056 mm.), and the rise to i*8 in 
the last half-hour is a difference such as occurs as a normal fluctuation 
under uniform conditions. 
Two of the experiments to be described later, on the Grand Period of 
growth, were also performed in darkness for comparison, and they showed 
no difference from those in light. The shoot was etiolated, but the rate of 
growth of the root was unaffected. Therefore, at least within the con- 
ditions under which all the rest of the experiments took place, light exerts 
no influence on the rate of growth. 
In the next place there is to be considered the effect of a sudden rise or 
fall of temperature. In all experiments the same results were found, namely 
that the roots assumed immediately on reaching the new temperature the 
rate of growth characteristic for it, and that, for temperatures up to 29 0 , such 
fluctuations as take place afterwards occur without showing either a typical 
time or mode of occurrence, so that, taking the mean of a number of peas, 
the rate of growth, for at least six hours, is represented by a straight line. 
To illustrate this the following experiments are quoted : 
1. Fall to low temper attire from thermostat temperature. 
Date. 
Time. 
Growth. 
Temperature. 
March 
7- 
2.27 p.m. to 2.57 p.m. 
o-i 
4’9° 
2.57 p.m. to 3.27 p.m. 
o-i 
March 
8. 
1 r. 42 a.m. to 12.12 p.m. 
o-i 
4*5° 
12.12 p.m. to 12.42 p.m. 
o-i 
4’5° 
12.42 p.m. to 1. 12 p.m. 
o-i 
4’5° 
March 
7- 
3.30 p.m. to 4 p.m. 
o-i 
4’9° 
4 p.m. to 4.30 p.m. 
0-2 
4*9° 
March 
4.30 p.m. to 5 p.m. 
0-2 
4*9° 
8. 
5 p.m. to 10.27 a.m. 
o-i i (mean) 
3’5° 
10.40 a.m. to n.ioa.m. 
o-i 
3*8° 
1 1. 10 a.m. to 11.40 a.m. 
0-2 
3-9° 
The fall here is from thermostat temperature, 15 0 to 17 0 , to about 4 0 . 
In both, the characteristic low rate of growth is assumed at once and 
maintained. In No. 2, where the growth during the night was measured, 
giving a mean rate of o-n, a fall is seen as compared with the rate from 
3.30 to 5, which is 0*17, due to the fall of temperature from 4-9° to 3-5° 
during the night. In No. 1 the rate on the 8th is the same as on the 
previous day, it being measured at nearly the same temperature. 
